In the third grant year it is proposed to continue and expand studies on the epidemiology of type B hepatitis. Through surveillance and case finding, the epidemiological patterns of occurrence and mode of spread of type B hepatitis will continue to be studied, with emphasis on the definition of mechanisms of transmission and the role of chronic HBsAg carriers in the dissemination of the disease. Comparable data will be obtained for type A hepatitis. The role of saliva as a vehicle of transmission of type B hepatitis will be investigated further. The infectivity potential of HBsAg carriers and acute hepatitis cases will be defined. Studies will be conducted on patterns of serologic response in type B hepatitis, including investigation of the behavior of surface and core antigen, e-antigen and e-antibody. The serologic studies of type B hepatitis will be continued. The investigation of anti-DNA in viral hepatitis will be pursued further.